Sampling saproxylic beetle assemblages in dead wood logs:: comparing window and eclector traps to traditional bark sieving and a refinement

The use of saproxylic beetle community as a metric to evaluate nature conservation measures in forests requires efficient methods. We first compare traditional bark sieving to a potential improvement (extracting beetles from whole bark with Tullgren funnels) to determine the most efficient. Secondly we compare this most efficient bark sampling to eclector and window traps. At the species, family, and functional group levels, we consider species richness, abundance and practical aspects. Traditional bark sieving missed > 50% of the individual beetles compared to whole bark sampling so we recommend the latter. Window traps caught large numbers of mobile saproxylic beetles, but a high proportion of non-saproxylics results in high sorting cost; bark sampling and eclector traps had a high proportion of saproxylics and obligate saproxylics. Compared to bark sampling, eclector traps are non-destructive, and monitor the whole saproxylic assemblage (i.e. also beetles inside the wood). Overall, window traps are useful because they capture saproxylic beetles attracted to dead wood and sample the local species pool, whereas eclector traps capture the saproxylics that actually emerge from a particular piece of dead wood, and thus are suited to detailed studies. Overall, we suggest that a combination of these two best methods is highly complementary.